光弹条纹图像的全场相移技术

本文详细分析了光弹性条纹图像的特点，利用图像处理技术，结合相移法及Ｔａｒｄｙ补偿法，实现了等倾线和等差线的全场相移，使得模型中任一点的主应力差值及第一主应力方向值可由计算机自动判读，实现了光弹性实验数据的自动处理。     

光弹等差线与等倾线参数的全场检测法

本文研究了一种自动获得全场等差线级数与等倾线参数角的方法.该方法是根据“相移”思想,利用数字图像处理技术,对光弹等差线图与等倾线图进行位相检测,经过去包裹处理,确定出全场各点的等差条纹级次与主应力方向角.最后通过典型实验,考核了这种方法的正确性与处理精度。     

单像素成像的数字光弹研究

数字光弹是光测力学中进行应力分析的重要方法,其核心是通过数字图像处理的方式确定等倾线和等差线参数并获得对应的相位图.传统的数字光弹使用面阵相机拍摄得到光弹性条纹图像,但是通常在特殊波段尤其是在非可见光波段中适用的面阵相机普遍比较昂贵、制造成本也相对较高.本文提出在数字光弹中引入一种具有低成本、高成像质量优势的成像方法—...     

数字光弹性法综述

将光弹性法与计算机图像处理技术相结合 ,来自动采集光弹性数据和分析应力的方法 ,称为数字光弹性法 ,与传统光弹性法相比 ,它可以进一步提高实验速度和精度。本文详细讨论了以下两个方面 :一是光弹性条纹的细化和倍增处理技术 ;二是自动确定光弹性参数的技术 ,包括相移法、傅立叶变换法、逐步载荷法、广谱分析法和RGB光弹性法等。通过对近二十年来国内外在这些方面的研究、应用和进展作了综述 ,认为采用白光的彩色域相移技术计算光弹性等倾角 ,结合采用白光源或三色光源的相移法来确定光弹性等色线级数 ,有望成为解决静态二维和三维冻结模型薄切片应力分析的最佳方法 ;另外 ,设计一种能实时和同步采集多幅条纹图的实验装置 ,通过相移法来自动获取动态光弹性数据 ,是数字动态光弹性法很有前景的发展方向     

基于动态光弹性方法的冲击载荷作用下自由边界主应力研究

当物体在冲击载荷作用下,物体内部会产生应力波,研究应力波的传播过程及规律对研究物体受冲击载荷作用具有重大的意义.应力波在物体内传播时,在自由边界处产生的主应力状态对于理论求解和计算有着重要意义.采用动态光弹性方法,结合新型动光弹系统及相关实验设备采集物体在冲击载荷作用下的等倾线和等差线条纹图,通过分析等倾线的条纹,得出等倾线与自由边界相交所成角度不为0°或909,得出在物体自由边界处两个主应力均存在且不为零的结论.针对上述结果,采用电测方法进行验证,两试验结果相符合,方案可行且准确.     

光弹性等倾线获取的图像处理技术

提出一种对数微分法,有效地解决了光弹性实验中等倾线的提取问题,不仅可消除平面偏振光场中等差线对等倾线的影响,而且能高精度地提取任意复杂受力模型等倾线.最后给出了等倾线提取及精度分析的两个实例,实验证明;本方法具有广阔的应用前景.     

斜拉桥塔锚固区光弹性应力分析与等倾线图像处理

本文采用光弹性冻结应力法，对独塔斜拉桥塔锚固区进行了应力分析，给出了有关截面的边界应力分布及主应力迹线，从而为优化工程设计提供了重要的参考依据。本文还提出了一种新的提取等倾线的方法──图像对数增强相减法，实现了等倾线与等差线条纹的分离，同时使条纹得到了细化，提高了处理等倾线的速度与准确度。编制了自动绘制主应力迹线的程序，利用它绘制了桥塔截面的次主应力迹线。     

数字图像处理技术用于等倾线条纹的处理

本文利用数字图像处理技术,对光弹性条纹进行处理,实现了等倾线与等差线的分离,提高了等倾线的测试精度。同时利用微机系统进行主应力迹线的绘制,提高了主应力迹线绘制的准确性.     

边界元法与光弹性实验相结合的应力分析法

本文介绍了边界无法与光弹性实验相结合进行应力分析的方法。叙述了用边界无法求解主应力的基本原理。结合光弹性实验等差线条纹图,可分离出主应力。     

法拉第效应在全息光弹中的应用

本文在应用前人提出的单独获得等差线或等和线的实验方法的基础上,进一步研究和应用了法拉第旋光效应分离条纹的结果.还提出并实验了一种新方法,即应用法拉第旋光器改变光弹性中及全息光弹性中使用手动或机械去测取等倾线以及对等差线小数级条纹补偿的习惯作法.     

Evaluation of Conformal and Non-Conformal Contact Parameters Using Digital Photoelasticity

Experimental studies to exploit photoelastic data of conformal geometries to extract contact parameters are non-existent because closed-form stress field equations were not available until recently. In this paper, the explicit equations recently reported in the literature for a flat punch with rounded edges are generalized so that a single set of equations can be used for a flat punch with rounded edges and Hertzian contacts with arbitrary radii of curvatures. The generality of the governing equations is verified by plotting isochromatics for conformal and non-conformal contact situations. A generic method to evaluate unknown contact parameters from the whole-field isochromatic data for conformal and non-conformal geometries is implemented. The methodology is initially verified using theoretically generated isochromatic data and is then used to experimentally evaluate two contact situations. In view of high-fringe gradient zones, the suitability of various digital photoelastic methods is compared. A novel four-step phase shifting technique is proposed in which isochromatic and isoclinic data can be evaluated using the minimum number of images.     

Real-time analysis of isochromatics and isoclinics using the phase-shifting method

This paper studies a new real-time phase-shifting method for the analysis of isochromatic and isoclinic parameters in photoelasticity. By rotating an analyzer at a constant rate and an output quarter-wave plate at a double rate of the analyzer and recording images by a CCD camera continuously, sequential images which brightness is integrated by sensors in a CCD camera during phase-shifting are obtained. Then, the distributions of the isochromatic and isoclinic parameters are obtained immediately and quantitatively using the proposed phase-shifting algorithm. The proposed method can be applied to high-speed inspection of optical elements or glass products. Also, it is expected that slowly varying time-dependent problems can be analyzed by the proposed method.     

Two-wavelength method for full-field automated photoelasticity

A new method for the whole-field determination of the isoclinic angle α and the isochromatic parameter ϕ is presented. The problems appearing during the calculation of these two parameters are solved with the use of two different wavelengths. Indeed, when a monochromatic light is used as an incident light, α is not measurable at the points where ϕ is equal to 2kπ. In this method, each monochromatic light can compensate for the influence of ϕ to obtain the isoclinic angle for the entire model. Also, most of the methods calculate the fractional fringe order that is unwrapped afterward to obtain the isochromatic parameter. This unwrapping process needs an initialization, which cannot be automatic with only one isochromatic fringe pattern. The use of two wavelengths permits a complete automatic unwrapping of the isochromatic parameter, even for the initialization of the process.     

Full-field automatic evaluation of an isoclinic parameter in white light

In this paper, a technique for full-field evaluation of the isoclinic parameter is presented. It combines the phase-shifting method with true color imaging technology to minimize the interaction between isoclinic and isochromatic fringes. The paper also shows how the proposed technique can be suitably integrated with known methods for evaluating the retardations. Furthermore, a digital algorithm for filtering wrapped phase data obtained by general phase-shifting techniques is presented.     

On the fiber-reinforced birefringent composite materials

The isochromatic and isoclinic parameters for fiber-reinforced birefringent materials are examined. Experimental results reveal residual birefringence and an initial isoclinic coincident with the axis of material symmetry. These preliminary data also indicate that the isoclinic angle is neither a measure of the principal strain nor the principal-stress directions within the composite.     

Phase-Multiplied Photoelastic and Series Interferometer Arrangement for Full-Field Stress Measurement in Single Crystals

A compact, phase-multiplied, circular polariscope and series interferometer arrangement is developed for high-resolution, full-field stress measurement in single crystals with weak piezo-optical coefficients. We present a general stress-optic law, derived from anisotropic piezo-optical constitutive relations, which provides the theoretical framework for obtaining stress field components from measured optical isoclinic, isochromatic and isopachic phase maps. A new phase image processing technique is also developed, which combines data obtained from different interference configurations for the successful removal of low-modulation zones within isoclinic and isopachic phase maps. The validity and accuracy of the proposed interferometer arrangement and stress measurement methodology are demonstrated through a compression test of a c-cut single crystal sapphire plate loaded by a cylindrical indenter.     

Phase-Stepping Photoelasticity by Use of Retarders with Arbitrary Retardation

The present paper describes a new phase-stepping algorithm for the analysis of isochromatics and isoclinics using retarders with arbitrary retardation. A retarder used in the proposed method is not necessarily a quarter-wave plate specified for the wavelength of the light used. Not only the isochromatic and isoclinic parameters but also the retardation of the input and output retarders are determined simultaneously by the proposed phase-stepping method. Thus, accurate analysis can be performed by the proposed method even if accurate quarter-wave plates are not used. In addition, any wavelength of visible light can be used in a single polariscope without requiring matching the wavelength of the quarter-wave plate. Thus, a multi-wavelength technique is easily combined with the proposed method for accuracy improvement, phase-unwrapping, or correction of ambiguity.     

Basic relations of photoelasticity

The polarization-optical method is used to study stresses and to measure the optical quantities (the isochromatic fringe orders and the isoclinic parameters) and the mechanical quantities (stresses and strains). The dependencies between these quantities are considered. The problem of disk compression along its diameter is solved exactly. These dependencies are analyzed on the basis of this exact solution and the experimental data. The most preferred form to express the basic relations of photoelasticity is discussed.     

Extension of oblique-incidence method to photo-orthotropic elasticity

With the interpretation of isochromatic and isoclinic fringes in transparent, birefringent, orthotropic composites established, efforts have been in progress to determine the-individual values of the principal stresses or strains. Several methods have recently been proposed. Some of them utilize the photoelastic results only partially and rely on numerical procedures. Others have attempted to obtain the required information based entirely on experimental data. In this paper, the classical oblique-incidence technique is applied to transversely isotropic-birefringent composites. The proposed extension is verified by applying it to the problem of an orthotropic half-plane subjected to an edge-load.